An infrastructure for supplying a hydrogen-containing gas used as a fuel at the time of power generation is not being developed as a typical material infrastructure, so that a fuel cell system typically includes a hydrogen generator including a reformer configured to generate a hydrogen-containing gas from a natural gas or LPG supplied from the typical material infrastructure.
A sulfur compound as an odorant may be added to the natural gas or LPG supplied from the typical material infrastructure, and the natural gas or LPG may originally contain a sulfur compound. Since the sulfur compound often poisons the catalyst that generates the hydrogen-containing gas, an adsorptive desulfurization catalyst or a hydrodesulfurization catalyst is provided upstream of the catalyst that generates the hydrogen-containing gas, to remove the sulfur compound. In many cases, the hydrodesulfurization catalyst having a high adsorption capacity and capable of realizing maintenance free is included in the hydrogen generator.
To generate the hydrogen-containing gas from the natural gas or the LPG, a steam-reforming reaction is typically used. In the steam-reforming reaction, for example, a city gas and steam that are materials are caused to react with each other at a high temperature of about 600° C. to 700° C. by using a precious metal-based reforming catalyst, such as a Ni-based reforming catalyst or a Ru-based reforming catalyst. Thus, the hydrogen-containing gas containing hydrogen as a major component is generated.
The hydrogen-containing gas contains CO (carbon monoxide), and the CO poisons a fuel cell to reduce the voltage of the fuel cell. Therefore, for example, a Cu-based shift catalyst is provided downstream of the reforming catalyst to reduce the CO by a water gas shift reaction. To further reduce the CO, a Ru-based or Pt-based selective oxidation catalyst or a Ni-based or Ru-based methanation catalyst is provided to reduce the CO to several hundred ppm to several ppm.
PTL 1 discloses a shift reaction portion including a high-temperature shift reaction portion configured to perform a high-temperature shift reaction that is a shift reaction at high temperatures (for example, 400° C. to 600° C.) and a low-temperature shift reaction portion configured to perform a low-temperature shift reaction that is a shift reaction at temperatures (for example, 150° C. to 350° C.) lower than the temperatures of the high-temperature shift reaction (paragraph 0023). In the low-temperature shift reaction portion, a reformed gas supplied through an upper side of an outer peripheral portion of the low-temperature shift reaction portion is caused to flow to a lower portion of the outer peripheral portion and then turns around to return through an inner peripheral portion of the low-temperature shift reaction portion to an upper portion of the low-temperature shift reaction portion to be introduced to the low-temperature shift catalyst portion (paragraph 0037).